Diuron
Trade Names: Karmex, Diurex
Registration status: This herbicide is not registered for use in tender fruit orchards.
When to suspect injury: New orchards planted into fields treated with high rates of diuron for several years (eg. following grapes, asparagus, gladioli) may show symptoms of stunting. Check for soil organic matter levels and a five-year herbicide history for the field.
Herbicide Information: Knowing how the herbicide works will help to determine the likelihood of injury from either direct application or drift. Consider how the herbicide works in plants, behaves in soils and what symptoms are common in other plants.
Chemical Family: Substituted urea
Site of Action/WSSA Group: Inhibitors of photosynthesis at photosystem II, Site B (alternate binding site) (WSSA Group 7)
General Symptoms in Plants
- Foliar chlorosis is concentrated around the veins, sometimes interveinal
- Necrosis of leaf tissue usually results over time
Symptoms in Tree Fruit
- Leaf veins turn yellow starting with the largest veins and progressing to the smallest
- Yellowing may spread to interveinal tissue, resembling simazine injury, and defoliation may occur
Uptake and Translocation
- Most readily absorbed by the roots, less so by the foliage
- Translocated upward in the plant in the xylem
Persistence
- At lower rates used in crops, residues last about a year
- If higher rates are used, residues can last longer
- Higher rates, and repeated use year-to-year may result in soil residues persisting for more than 1 year
If you suspect herbicide injury, laboratory analyses of herbicide levels in plant tissue are necessary to confirm the presence of herbicides, although symptoms may be helpful in diagnosing which herbicides caused the problem.
Both damaged and healthy plant tissues should be analyzed, because comparison levels are not readily available for many herbicides. Contact your lab for instructions on which plant parts should be sampled, how to handle and ship the sample, and what costs are involved to ensure an accurate and timely diagnosis.
